When I first heard about Deis it was heavily compared to Flynn [1]. It's a little hard to tell from the outside if the two are still competitors or if Deis is focusing on a lower level of abstraction.
I evaluated Flynn, Deis and Dokku and wasn't entirely satisfied with any of them opting for Heroku instead.
I've promised people a blogpost on this and I will do it once I get time to evaluate RancherOS too.
I also started with Deis and move on to k8s later on.